Abstract

The magnetic field dependence of dielectricpermittivity and resistivity has been measured simultaneously in two separate half doped manganites Pr0.75Na0.25MnO3 and Pr0.5Ca0.5Mn0.975Al0.025O3. A gigantic change in dielectricpermittivity was detected near the percolation threshold. The hysteresis in dielectricpermittivity as well as in resistivity supports the first order nature of the insulator-metal transition while the tunability is due to the coexisting of phases across the transition. A highly resistivity correlated dielectric behaviour has been observed throughout the insulator to metal transition evidencing the dielectric catastrophe phenomenon. The field dependent dielectric data are analyzed in the framework of Maxwell-Garnett theory in association with Mott-Hubbard model.